Such a work tool is known from DE 296 15 157 U1. Here two toggle levers pivotably grip directly onto the end of the piston rod in the head housing. Two gripper arms are pivotable between a closed position and an opened position. In the closed position, the gripper arms are arranged parallel to each other. A bearing axis arranged in the region of the free end of the piston rod for the two toggle levers is provided at the end with bearing rollers which are guided in guide grooves of the head housing.
Because of the direct connection of the toggle levers to the piston rod, the opening angle of the gripper arms is not adjustable. Also, this design does not allow particularly large opening angles of the gripper arms because the piston rod protrudes into the movement path of the center joint of the toggle lever.
Also, with this work tool the free end of the piston rod is guided via the axis passing through this, which simultaneously forms the bearing axis of the toggle levers. In this work tool, the length of the piston rod is not adjustable. Thus the opening angle of the arms is also not adjustable.
Pneumatically operable work tools with gripper or clamping arms using a piston rod which is not adjustable in length are also known from DE 10 2004 040 606 B3, EP 2 241 402 A1 and US RE 41,223 E.
EP 2 548 700 A1 describes a pneumatically operable work tool in which, in an opened position of a clamping arm, a piston of a cylinder is positioned in the region of a base of the cylinder housing. To be able to adjust the opening angle of the clamping arm, the piston rod is designed adjustable in length and has piston rod parts with threaded positions, wherein the piston rod parts are screwed into each other. By twisting the piston rod part facing the base of the cylinder housing, when the piston is arranged in the region of the base, the length of the piston rod can be changed using means accessible from the outside to turn the piston rod part, and hence the opening angle of the clamping arm can be adjusted continuously.